Defect inspection apparatus and defect inspection method

ABSTRACT

A defect inspection apparatus includes: an illumination unit configured to illuminate an inspection object region of a sample with light emitted from a light source; a detection unit configured to detect scattered light in a plurality of directions, which is generated from the inspection object region; a photoelectric conversion unit configured to convert the scattered light detected by the detection unit into an electrical signal; and a signal processing unit configured to process the electrical signal converted by the photoelectric conversion unit to detect a defect in the sample. The detection unit includes an imaging unit configured to divide an aperture and form a plurality of images on the photoelectric conversion unit. The signal processing unit is configured to synthesize electrical signals corresponding to the plurality of formed images to detect a defect in the sample.

TECHNICAL FIELD

The present invention relates to a defect inspection apparatus and adefect inspection method.

BACKGROUND ART

In order to maintain or enhance a yield of a product in a manufacturingline for a semiconductor substrate, a thin film substrate or the like,inspection of a defect that exists on a surface of the semiconductorsubstrate, the thin film substrate or the like is performed.

For example, Patent Literature 1 describes a technique for inspectingsuch a defect. In Patent Literature 1, in order to accurately detect asmall number of photons from an infinitesimal defect, a large number ofpixels are arrayed to form a sensor. Then, total pulse currentsgenerated by incidence of photons on each pixel arrayed in the sensorare measured to detect the infinitesimal defect.

PRIOR ART LITERATURE Patent Literature

PTL 1: JP-A-2013-231631

SUMMARY OF INVENTION Technical Problem

For defect inspection used in a manufacturing process of a semiconductoror the like, it is important to detect the infinitesimal defect withhigh accuracy.

In Patent Literature 1, a detection system including a smaller apertureis arranged such that a longitudinal direction of an image obtained bylinear illumination is imaged on a sensor. However, when the detectionsystem is arranged at a position where an optical axis of the detectionsystem is not orthogonal to the longitudinal direction of the linearillumination during image formation in the longitudinal direction of theimage, optical distance to a surface of a sample is not constant at acenter of a visual field and an edge of the visual field of eachdetection system. Therefore, it is necessary to dispose the optical axisof the detection system in a direction orthogonal to the longitudinaldirection of the linear illumination.

However, it is difficult to completely capture scattered light from thesurface of the sample with such an arrangement, and the number ofphotons is insufficient to detect the infinitesimal defect. As a result,it is difficult to detect an infinitesimal defect that exists on thesurface of the sample with high accuracy.

An object of the present invention is to detect a defect that exists ona surface of a sample with high accuracy by a defect inspectionapparatus.

Solution to Problem

A defect inspection apparatus according to an aspect of the presentinvention includes: an illumination unit configured to illuminate aninspection object region of a sample with light emitted from a lightsource; a detection unit configured to detect scattered light in aplurality of directions, which is generated from the inspection objectregion; a photoelectric conversion unit configured to convert thescattered light detected by the detection unit into an electricalsignal; and a signal processing unit configured to process theelectrical signal converted by the photoelectric conversion unit todetect a defect in the sample. The detection unit includes an imagingunit configured to divide an aperture and form a plurality of images onthe photoelectric conversion unit. The signal processing unit isconfigured to synthesize electrical signals corresponding to theplurality of formed images to detect a defect in the sample.

A defect inspection method according to an aspect of the presentinvention includes: an illumination step of illuminating an inspectionobject region of a sample with light emitted from a light source; alight detection step of detecting scattered light in a plurality ofdirections, which is generated from the inspection object region; aphotoelectric conversion step of converting the detected scattered lightby a photoelectric conversion unit into an electrical signal; and adefect detection step of processing the converted electrical signal todetect a defect of the sample. An aperture of an imaging unit is dividedto form a plurality of images on the photoelectric conversion unit inthe light detection step. Electrical signals corresponding to theplurality of formed images are synthesized to detect a defect of thesample in the defect detection step.

Advantageous Effect

According to one aspect of the present invention, the defect that existson the surface of the sample can be detected with high accuracy by thedefect inspection apparatus.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an overall schematic configuration diagram showing a defectinspection apparatus according to an embodiment.

FIG. 2 is a diagram showing a first example of an illumination intensitydistribution pattern realized by an illumination unit.

FIG. 3 is a diagram showing a second example of an illuminationintensity distribution pattern realized by the illumination unit.

FIG. 4 is a diagram showing a third example of an illumination intensitydistribution pattern realized by the illumination unit.

FIG. 5 is a diagram showing a fourth example of an illuminationintensity distribution pattern realized by the illumination unit.

FIG. 6 is a diagram showing a fifth example of an illumination intensitydistribution pattern realized by the illumination unit.

FIG. 7 is a diagram showing a first example of an optical elementprovided in an illumination intensity distribution control unit.

FIG. 8 is a diagram showing a first example that shows an illuminationdistribution pattern and a scanning direction on a surface of a sample.

FIG. 9 is a diagram showing a first example of a locus of a light spotformed by scanning.

FIG. 10 is a view of arrangement of a detection unit and detectiondirections as viewed from the side.

FIG. 11 is a view of arrangement of a low-angle detection unit anddetection directions as viewed from above.

FIG. 12 is a view of arrangement of a high-angle detection unit anddetection directions as viewed from above.

FIGS. 13A and 13B are diagrams showing a first example of aconfiguration of the detection unit.

FIGS. 14A and 14B are diagrams showing a first example of aconfiguration of an imaging optical system to a photoelectric conversionunit.

FIG. 15 is a diagram showing a coordinate system of the detection unit.

FIG. 16 is a diagram showing a first example of the photoelectricconversion unit.

FIG. 17 is a diagram showing a first example of an equivalent circuit ofcomponents of the photoelectric conversion unit.

FIG. 18 is a block diagram showing an example of a data processing unit.

FIGS. 19A and 19B are diagrams showing a second example of aconfiguration of a detection unit.

FIG. 20 is a diagram showing a second example of a photoelectricconversion unit.

FIG. 21 is a diagram showing a second example of an equivalent circuitof components of the photoelectric conversion unit.

FIG. 22 is a diagram showing a first example of an equivalent circuit ofan integrated part of output signals of the photoelectric conversionunit.

FIG. 23 is a diagram showing a third example of a photoelectricconversion unit.

FIG. 24 is a diagram showing a third example of an equivalent circuit ofcomponents of the photoelectric conversion unit.

FIGS. 25A, 25B, and 25C are diagrams showing a second example of aconfiguration of a detection unit.

FIG. 26 is a diagram showing a second example of a scanning direction onthe surface of the sample.

FIG. 27 is a diagram showing a third example of a configuration of adetection unit.

FIG. 28 is a diagram showing an optical path branching mirror as aconfiguration of the detection unit.

FIG. 29 is a diagram showing a configuration example of a lens array.

FIG. 30 is a diagram showing a configuration example of a multi-channelTDI sensor.

FIG. 31 is a diagram showing an embodiment of an arrangement of the lensarray.

FIGS. 32A and 32B are diagrams showing an example of a configuration ofthe detection unit.

FIG. 33 is a graph showing an intensity profile of an image formed bythe detection unit.

FIG. 34 is a graph showing an intensity profile of an image formed bythe detection unit.

FIG. 35 is a graph showing an intensity profile of an image formed bythe detection unit.

FIGS. 36A, 36B, and 36C are diagrams showing an example of aconfiguration of a detection unit.

FIG. 37 is a diagram showing an example of a configuration of adetection unit.

FIG. 38 is a diagram showing an example of a configuration of adetection unit.

FIG. 39 is a diagram showing an example of a configuration of adetection unit.

DESCRIPTION OF EMBODIMENTS

In the following embodiments, a defect inspection apparatus used fordefect inspection performed in a manufacturing process of asemiconductor or the like will be described as an example. The defectinspection apparatus is used to achieve the following aspects: detectingof an infinitesimal defect, measuring of dimensions of the detecteddefect with high accuracy, nondestructive inspecting of a sample(without converting a property of the sample), acquiring of fixedinspection results substantially with regard to the number, positions,dimensions, and defect types of detected defects, inspecting of a largenumber of samples within fixed time, and the like.

First Embodiment

A configuration of a defect inspection apparatus according to a firstembodiment will be described with reference to FIG. 1.

As shown in FIG. 1, the defect inspection apparatus includes anillumination unit 101, a detection unit 102, a photoelectric conversionunit 103, a stage 104 on which a sample W can be placed, a signalprocessing unit 105, a control unit 53, a display unit 54, and an inputunit 55. The illumination unit 101 includes, as appropriate, a lasersource 2, an attenuator 3, an outgoing beam adjustment unit 4, a beamexpander 5, a polarization control unit 6, and an illumination intensitydistribution control unit 7.

A laser beam emitted from the laser source 2 is adjusted to have desiredbeam intensity by the attenuator 3, the laser beam is adjusted to reacha desired beam position and travel in a desired beam travel direction bythe outgoing beam adjustment unit 4, the laser beam is adjusted to havea desired beam diameter by the beam expander 5, the laser beam isadjusted to be in a desired polarization state by the polarizationcontrol unit 6, the laser beam is adjusted to exhibit desired intensitydistribution by the illumination intensity distribution control unit 7,and an inspection object region of the sample W is irradiated with thelaser beam.

An incidence angle of illumination light relative to a surface of asample is determined by a position and an angle of a reflecting mirrorof the outgoing beam adjustment unit 4 arranged in an optical path ofthe illumination unit 101. The incidence angle of the illumination lightis set to an angle suitable for detecting an infinitesimal defect. Thelarger the illumination incidence angle is, that is, the smaller anillumination elevation angle (an angle between the surface of the sampleand an illumination optical axis) is, the weaker scattered light (calledhaze) from minute irregularities on the surface of the sample, which isa noise, is, in relation to scattered light from a minute foreign matteron the surface of the sample, which is suitable for detection of aninfinitesimal defect. Therefore, when the scattered light from theminute irregularities of the surface of the sample interferes with thedetection of an infinitesimal defect, the incidence angle of theillumination light is preferably set to 75 degrees or more (15 degreesor less in terms of the elevation angle).

Meanwhile, when the shortage of the quantity of scattered light from adefect interferes with the detection of the infinitesimal defect, theincidence angle of the illumination light is preferably set 60 degreesor more and 75 degrees or less (15 degrees or more and 30 degrees orless in terms of the elevation angle) because, in oblique incidentillumination, the smaller the incidence angle of the illumination lightis, the more an absolute quantity of scattered light from a minuteforeign matter is. In oblique incident illumination, the illuminationlight is polarized to p-polarized light under polarization control ofthe polarization control unit 6 of the illumination unit 101, and thusscattered light from a defect on the surface of the sample increasescompared with other polarized light. In addition, when the scatteredlight from minute irregularities of the surface of the sample interfereswith the detection of an infinitesimal defect, the illumination light ispolarized to s-polarized light, and thus scattered light from the minuteirregularities of the surface of the sample decreases compared withother polarized light.

If necessary, as shown in FIG. 1, an optical path of illumination lightis changed by placing a mirror 21 in an optical path of the illuminationunit 101 and arranging other mirrors appropriately, and the illuminationlight is emitted from a direction substantially perpendicular to thesurface of the sample (vertical illumination). At this time,illumination intensity distribution on the surface of the sample iscontrolled, as in a case of the oblique incident illumination, by anillumination intensity distribution control unit 7 v. In order toacquire the oblique incident illumination and scattered light from aconcave defect (a flaw by polishing and a crystal defect due to crystalmaterials) on the surface of the sample by placing a beam splitter inthe same position as the mirror 21, the vertical illumination in whichillumination light is emitted substantially perpendicularly to thesurface of the sample is suitable.

As the laser source 2, one that oscillates an ultraviolet or vacuumultraviolet laser beam having a short wavelength (355 nm or less) as awavelength difficult to penetrate an inside of the sample and outputsthe laser beam of 2 W or more is used for detecting an infinitesimaldefect in a vicinity of the surface of the sample. A diameter of anoutgoing beam is about 1 mm. In order to detect a defect inside thesample, a laser source is used which oscillates a visible or infraredlaser beam having a wavelength easy to penetrate the inside of thesample.

The attenuator 3 includes, as appropriate, a first polarizing plate, ahalf-wave plate rotatable around an optical axis of the illuminationlight, and a second polarizing plate. The light incident on theattenuator 3 is converted to linearly polarized light by the firstpolarizing plate with a direction of the polarization being rotated toany direction in accordance with an azimuth angle of a slow axis of thehalf-wave plate, and the light passes through the second polarizingplate. Light intensity is dimmed at any ratio by controlling the azimuthangle of the half-wave plate. When a degree of linear polarization oflight incident on the attenuator 3 is sufficiently high, the firstpolarizing plate is not necessarily required. For the attenuator 3, onein which a relationship between an input signal and a dimming rate iscalibrated beforehand is used. As the attenuator 3, it is possible touse an ND filter having gradated density distribution and to use andswitch a plurality of ND filters having mutually different density.

The outgoing beam adjustment unit 4 includes a plurality of reflectingmirrors. Here, an embodiment in which the emission light adjustment unit4 is configured with two reflecting mirrors will be described. However,the invention is not limited thereto, and three or more reflectingmirrors may also be appropriately used. Here, it is assumed that athree-dimensional rectangular coordinate system (XYZ coordinates) isdefined, and incident light on the reflecting mirror is traveling in a+X direction. The first reflecting mirror is installed such that theincident light is deflected in a +Y direction (which means the incidenceand reflection of light occurs in an XY plane). The second reflectingmirror is installed such that the light reflected by the firstreflecting mirror is deflected in a +Z direction (which means theincidence and reflection of light occurs in a YZ plane).

A position and a traveling direction (an angle) of light emitted fromthe outgoing beam adjustment unit 4 are adjusted by paralleldisplacement and adjustment of a tilt angle each reflecting mirror. Whenthe incidence and reflection surface (the XY plane) of the firstreflecting mirror is orthogonal to the incidence and reflection surface(the YZ plane) of the second reflecting mirror as described above,adjustment of a position and an angle on an XZ plane and adjustment of aposition and an angle on the YZ plane of light (traveling in the +Zdirection) emitted from the outgoing beam adjustment unit 4 can beindependently performed.

The beam expander 5 includes two or more groups of lens, and has afunction of magnifying a diameter of an incident parallel light beam.For example, a Galileo beam expander including a combination of aconcave lens and a convex lens is used. The beam expander 5 is installedon a translation stage having two or more axes, and the adjustment ofthe position is possible such that a predetermined beam position and thecenter are coincident. In addition, the beam expander 5 has a functionof adjusting a tilt angle of the entire beam expander 5 such that anoptical axis of the beam expander 5 and a predetermined beam opticalaxis are coincident. The magnification of a diameter of a light beam canbe controlled by adjusting an interval between the lenses (a zoommechanism).

When light incident on the beam expander 5 is not parallel, themagnification of the diameter of the beam and collimation (thesemi-parallelization of a light beam) is simultaneously performed byadjusting the interval between the lenses. The collimation of the lightbeam may be performed by installing a collimator lens on an upstreamside of the beam expander 5 independently of the beam expander 5. Themagnification of a beam diameter caused by the beam expander 5 is about5 to 10 times, and a beam emitted from the light source and having abeam diameter of 1 mm is magnified to have a diameter of about 5 mm to10 mm.

The polarization control unit 6 is configured with a half-wave plate anda quarter-wave plate, and controls a polarization state of illuminationlight to be any polarization state. On the way of the optical path ofthe illumination unit 101, a state of light incident on the beamexpander 5 and a state of light incident on the illumination intensitydistribution control unit 7 are measured by a beam monitor 22.

FIGS. 2 to 6 schematically show a positional relationship between anillumination optical axis 120 guided from the illumination unit 101 tothe surface of the sample and an illumination intensity distributionpattern. It should be noted that the configuration of the illuminationunit 101 shown in FIGS. 2 to 6 is a part of the configuration of theillumination unit 101, and the outgoing beam adjustment unit 4, themirror 21, the beam monitor 22, and the like are omitted.

FIG. 2 schematically shows a cross section of an incidence plane (aplane including the optical axis of illumination and the normal of thesurface of the sample) of oblique incident illumination. In the obliqueincident illumination, the incident light is inclined relative to thesurface of the sample within the incidence plane. The illumination unit101 creates a substantially uniform illumination intensity distributionon the incidence plane. A length of a part where illumination intensityis uniform is about 100 μm to 4 mm so as to inspect a large region perunit time.

FIG. 3 schematically shows a cross section of a plane that includes anormal of the surface of the sample and is perpendicular to an incidenceplane in the oblique incident illumination. On this plane, illuminationintensity on the surface of the sample is distributed such that theintensity of the periphery is weaker compared with that of the center.More specifically, the illumination intensity distribution is Gaussiandistribution that reflects the intensity distribution of the lightincident on the illumination intensity distribution control unit 7, orintensity distribution similar to a primary Bessel function of the firstkind or a sinc function that reflects a shape of an aperture of theillumination intensity distribution control unit 7. In order to reducethe haze generated from the surface of the sample, the length ofillumination intensity distribution (a length of a region having thehighest illumination intensity of 13.5% or more) on this plane isshorter than the length of the part where the illumination intensity onthe incidence plane is uniform, and is about 2.5 μm to 20 μm. Theillumination intensity distribution control unit 7 includes opticalelements such as an aspherical lens, a diffractive optical element, acylindrical lens array, and a light pipe, which will be described below.As shown in FIGS. 2 and 3, the optical elements constituting theillumination intensity distribution control unit 7 are installedperpendicularly to the illumination optical axis.

The illumination intensity distribution control unit 7 includes anoptical element that acts on phase distribution and intensitydistribution of the incident light. As the optical element constitutingthe illumination intensity distribution control unit 7, a diffractiveoptical element 71 (DOE) is used (see FIG. 7).

The diffractive optical element 71 is obtained by forming a minuteundulating shape having a dimension equal to or smaller than awavelength of light on a surface of a substrate formed of materials thattransmit incident light. As a material that transmits incident light,fused quartz is used in a case where an ultraviolet light is used forthe illumination. In order to inhibit attenuation of light caused bytransmission through the diffractive optical element 71, a diffractiveoptical element to which a reflection reducing coating is applied ispreferably used. For the formation of the minute undulating shape,lithography process is used.

Quasi-parallel light obtained by the light passing through the beamexpander 5 passes through the diffractive optical element 71, so thatillumination intensity distribution on the surface of the sampleaccording to the undulating shape of the diffractive optical element 71is formed. The undulating shape of the diffractive optical element 71 isdesigned and produced to a shape determined based on calculation usingFourier optical theory so that the illumination intensity distributionformed on surface of the sample has long uniform distribution on theincidence plane.

The optical element provided in the illumination intensity distributioncontrol unit 7 includes a translation adjustment mechanism having two ormore axes and a rotation adjustment mechanism having two or more axes sothat a position and an angle relative to the optical axis of theincident light can be adjusted. Further, a focus adjustment mechanismbased on a movement in a direction of the optical axis direction isprovided. As an alternative optical element having a function similar tothe diffractive optical element 71, an aspherical lens, a combination ofa cylindrical lens array and a cylindrical lens, or a combination of alight pipe and an imaging lens may be used.

A state of illumination light in the illumination unit 101 is measuredby the beam monitor 22. The beam monitor 22 measures and outputs aposition and an angle (a traveling direction) of the illumination lightthat passes the outgoing beam adjustment unit 4, or a position and awave front of the illumination light incident on the illuminationintensity distribution control unit 7. The measurement of the positionof the illumination light is performed by measuring a position of acenter of gravity of the light intensity of the illumination light. As aspecific position measurement unit, a position sensitive detector (PSD)or an image sensor such as a CCD sensor and a CMOS sensor is used.

The measurement of an angle of the illumination light is performed bythe position sensitive detector or the image sensor which is installedin a position farther from the light source than the positionmeasurement unit or installed in a converging position of a collimatorlens. The position and the angle of the illumination light detected bythe sensor are input to the control unit 53 and are displayed on thedisplay unit 54. When the position or the angle of the illuminationlight is deviated from a predetermined position or angle, the outgoingbeam adjustment unit 4 is adjusted such that the illumination light isreturned to the predetermined position.

The measurement of the wave front of the illumination light is performedto measure a degree of parallelization of light incident on theillumination intensity control unit 7. Measurement by a shearinginterferometer or measurement by a Shack-Hartmann wave front sensor isperformed. The shearing interferometer measures a state of diverges orconverges of the illumination light by observing a pattern of aninterference fringe formed by projecting on a screen both of a reflectedlight from a front surface of an optical glass and a reflected lightfrom a back surface of the optical glass. In the shearinginterferometer, the optical glass is placed by obliquely tilting in theoptical path of illumination light and has a thickness of approximatelyseveral mm with both surfaces polished flatly. An example of theshearing interferometer includes SPUV-25 manufactured by SIGMA KOKI, orthe like. When an image sensor such as a CCD sensor and a CMOS sensor isinstalled in the position of the screen, the state in which illuminationlight diverges or converges can be automatically measured.

The Shack-Hartmann wave front sensor divides a wave front by the minutelens array and projects the divided wave front to an image sensor suchas a CCD sensor, and measures inclination of an individual wave frontbased on a displacement of a projection position. Compared with theshearing interferometer, detailed wave front measurement such as partialdisturbance of a wave front can be performed by using the Shack-Hartmannwave front sensor. When it is ascertained by the wave-front measurementthat the light incident on the illumination intensity control unit 7 isnot a quasi-parallel light but a diverged light or a converged light,the incident light can be arranged to approach the quasi-parallel lightby displacing the lens groups of the beam expander 5 on the upstreamside, in the direction of the optical axis.

When it is ascertained by the wave-front measurement that the wave frontof the light incident on the illumination intensity control unit 7 ispartially tilted, the wave front can be adjusted to be approximatelyflat by placing a spatial light phase modulation element, which is onetype of spatial light modulator (SLM), on the upstream side of theillumination intensity control unit 7 and applying appropriate phasedifference to each position on a cross section of a light beam such thatthe wave front is flat. That is, illumination light can be made toapproximate the quasi-parallel light. The wave front accuracy(displacement from a predetermined wave front (a designed value or aninitial state)) of the light incident on the illumination intensitydistribution control unit 7 is reduced to λ/10 rms or less by theabove-described wave front accuracy measurement/adjustment units.

The illumination intensity distribution on the surface of the sample,which is adjusted by the illumination intensity distribution controlunit 7, is measured by an illumination intensity distribution monitor24. As shown in FIG. 1, when vertical illumination is used, theillumination intensity distribution on the surface of the sample, whichis adjusted by the illumination intensity distribution control unit 7 v,is also measured by the illumination intensity distribution monitor 24similarly. The illumination intensity distribution monitor 24 images thesurface of the sample on an image sensor such as a CCD sensor and a CMOSsensor via a lens and detects the illumination intensity distribution onthe surface of the sample as an image.

The image of the illumination intensity distribution detected by theillumination intensity distribution monitor 24 is processed by thecontrol unit 53, a position of the center of gravity of intensity,maximum intensity, a maximum intensity position, the width and thelength of illumination intensity distribution (the width and the lengthof an illumination intensity distribution region having a predeterminedratio equal to or higher than a predetermined intensity or equal to orhigher than maximum intensity value), and the like are calculated, andare displayed together with a contour of the illumination intensitydistribution and a sectional waveform thereof on the display unit 54.

In the case of oblique incident illumination, the disturbance ofillumination intensity distribution due to the displacement of aposition of the illumination intensity distribution and defocusing iscaused by the displacement in height of the surface of the sample. Inorder to prevent the problem, the height of the surface of the sample ismeasured, and when the height is deviated, the deviation is corrected bythe illumination intensity distribution control unit 7 or by theadjustment of height in a Z axis of the stage 104.

The illumination distribution pattern (a light spot 20) formed on thesurface of the sample by the illumination unit 101 and a sample scanningmethod will be described with reference to FIGS. 8 and 9, respectively.

As the sample W, a circular semiconductor silicon wafer is assumed. Thestage 104 includes a translation stage, a rotation stage, and a Z stagefor adjusting the height of the surface of the sample (all not shown).The light spot 20 has illumination intensity distribution longitudinalin one direction as described above. The longitudinal direction isdefined as S2, and a direction substantially orthogonal to S2 is definedas S1. The sample is scanned in a circumferential direction S1 of acircle having a rotation axis of the rotating stage as the center, byrotational movement of the rotation stage, and is scanned in atranslation direction S2 of a translation stage by translation movementof the translation stage. The light spot draws a spiral locus T on thesample W by scanning, in the scanning direction S2, by distance equal toor shorter than the length of the light spot 20 in a longitudinaldirection while the sample is rotated once by scanning in the scanningdirection S1, and an entire surface of the sample 1 is scanned.

A plurality of detection units 102 are arranged to detect scatteredlight in a plurality of directions generated from the light spot 20.Examples of the arrangement of the detection units 102 relative to thesample W and the light spot 20 will be described with reference to FIGS.10 to 12.

FIG. 10 shows the arrangement of the detection units 102. An angleformed between a normal of the sample W and a detection direction basedon the detection unit 102 (a center direction of an aperture fordetection) is defined as a detection zenithal angle. The detection unit102 includes, as appropriate, a high-angle detection unit 102 h having adetection zenithal angle of 45 degrees or less and a low-angle detectionunit 1021 having a detection zenithal angle of 45 degrees or more. Aplurality of high-angle detection units 102 h and a plurality oflow-angle detection units 102 l are provided so as to cover scatteredlight scattered in many directions at each detection zenithal angle.

FIG. 11 is a plan view showing an arrangement of the low-angle detectionunit 102 l. An angle between the traveling direction of oblique incidentillumination and the detection direction on a plane parallel to thesurface of the sample W is defined as a detection azimuth angle. Thelow-angle detection unit 102 includes, as appropriate, a low-angle frontdetection unit 102 lf, a low-angle lateral side detection unit 102 ls,and a low-angle back detection unit 102 lb, as well as a low-angle frontdetection unit 102 lf′, a low-angle lateral side detection unit 102 ls′,and a low-angle back detection unit 102 lb′ which are respectivelylocated in positions symmetric to former detection units in relation toan illumination incidence plane. For example, the low-angle frontdetection unit 102 lf is installed such that a detection azimuth anglethereof is 0 degree or more and 60 degrees or less. The low-anglelateral side detection unit 1021 s is installed such that a detectionazimuth angle thereof is 60 degrees or more and 120 degrees or less. Thelow-angle back detection unit 102 lb is installed such that a detectionazimuth angle thereof is 120 degrees or more and 180 degrees or less.

FIG. 12 is a plan view showing an arrangement of the high-angledetection unit 102 h. The high-angle detection unit 102 includes, asappropriate, a high-angle front detection unit 102 hf, a high-anglelateral side detection unit 102 hs, a high-angle back detection unit 102hb, and a high-angle lateral side detection unit 102 hs′ located in aposition symmetric to the high-angle lateral side detection unit 102 hsin relation to the illumination incidence plane. For example, thehigh-angle front detection unit 102 hf is installed such that adetection azimuth angle thereof is 0 degree or more and 45 degrees orless. The high-angle back detection unit 102 hb is installed such that adetection azimuth angle thereof is 135 degrees or more and 180 degreesor less. Here, the case where four high-angle detection units 102 h areprovided and six low-angle detection units 102 l are provided isdescribed above, but the invention is not limited thereto. The numberand positions of the detection units may be changed as appropriate.

A specific configuration of the detection unit 102 will be describedwith reference to FIGS. 13A and 13B.

As shown in FIGS. 13A and 13B, scattered light generated from the lightspot 20 is converged by an objective lens 1021, and a polarizationdirection of the scattered light is controlled by a polarization controlfilter 1022. As the polarization control filter 1022, a half-wave platewhose rotation angle can be controlled by a drive mechanism such as amotor is used. In order to efficiently detect the scattered light, anumerical aperture (NA) for detection of the objective lens 1021 ispreferably 0.3 or more. In the case of the low-angle detection unit, alower end of the objective lens is cut off if necessary so that theinterference of the lower end of the objective lens 1021 with thesurface of the sample W is avoided. An imaging lens 1023 images thelight spot 20 in a position of an aperture 1024.

The aperture 1024 is an aperture that is set to allow passing of onlythe light in a region to be converted by the photoelectric conversionunit 103 among formed images of the beam spot 20. When the light spot 20has a Gaussian distribution profile in the S2 direction, the aperture1024 allows only a central portion having a large quantity of light inthe S2 direction in the Gaussian distribution to pass through, andshields a region in the Gaussian distribution where the quantity oflight in a beam end is small.

A disturbance such as air scattering is prevented which occurs when theillumination with the same size as the formed image of the light spot 20in the direction S1 transmits through air. A condenser lens 1025converges the formed image of the aperture 1024 again.

A polarization beam splitter 1026 separates, according to polarizationdirections, the light whose polarization direction is converted by thepolarization control filter 1022. A diffuser 1027 absorbs light in apolarization direction which is not used for photoelectric conversion inthe photoelectric conversion unit 103. A lens array 1028 forms images ofthe beam spot 20 on the photoelectric conversion unit 103 correspondingto the number of arrays.

In the embodiment, only light in a specific polarization direction amongthe light converged by the objective lens 1021 is photoelectricallyconverted by the photoelectric conversion unit 103 via a combination ofthe polarization control filter 1022 and the polarization beam splitter1026. As an alternative example, for example, the polarization controlfilter 1022 may be a wire grid polarizer having a transmittance of 80%or higher, so that light in a desired polarization direction can beobtained without using the polarization beam splitter 1026 and thediffuser 1027.

FIG. 14A includes a schematic diagram of the light spot 20 on the sampleW and FIG. 14B is a correspondence with the imaging from the lens array1028 to the photoelectric conversion unit 103.

As shown in FIG. 14A, the light spot 20 extends long in the direction S2of FIG. 8. W0 indicates a defect to be detected. The photoelectricconversion unit 103 divides the light spot into W-a to W-d and detectsthe divided light spots. Here, the light spot is divided into fourparts, but the present invention is not limited to this number. Thepresent invention may be embodied by setting the number of divisions toany integer.

As shown in FIG. 14B, scattered light from W0 is converged by theobjective lens 1021 and guided to the photoelectric conversion unit 103.The lens array 1028 is configured with cylindrical lenses that imageonly in one direction. In the photoelectric conversion unit 103, pixelblocks 1031, 1032, 1033, and 1034 corresponding to the number of arraysof the lens array 1028 are arranged. Since the region where the quantityof light is small and the photoelectric conversion is not performed isshielded by the aperture 1024, the pixel blocks 1031 to 1034 can bearranged close to each other. The lens array 1028 is placed at aposition where a pupil of the objective lens 1021 is relayed. In orderto form an image for each of divided pupil regions, the image formed bythe lens array 1028 is narrowed by narrowing the aperture, and depth ofa focus is increased. As a result, imaging detection is possible from adirection that is not orthogonal to S2.

Here, an effect of the lens array 1028 will be described in more detailwith reference to FIG. 31. The condenser lens 1025 has a large numericalaperture that is generally equal to the numerical aperture of theobjective lens 1021. The condenser lens 1025 having a large numericalaperture converges light scattered in various directions, which reducesthe depth of the focus. When an optical axis of the objective lens 1021is not orthogonal to S2 that is a longitudinal direction of theillumination, optical distance varies at a center of a visual field andan edge of the visual field, and an image formed on the photoelectricconversion unit 103 is defocused.

As shown in FIG. 31, the lens array 1028 is placed at a pupil positionof the condenser lens 1025. In other words, the lens array 1028 isplaced at a position where a pupil of the objective lens 1021 isrelayed. Further, in other words, the lens array 1028 is located at arear focal position of the condenser lens 1025. The condenser lens 1025has a size equal to a pupil diameter so that all light incident on theaperture diameter of the objective lens 1021 can be imaged ideally.

At the position of the lens array 1028, light having an incidentdirection similar to an incident direction towards the condenser lens1025 is distributed to be close to each other. As a result, when thelens array 1028 is placed at this position, the numerical aperture isreduced, and the depth of the focus may be increased. In this way, thepupil region is divided so as to reduce the numerical aperture, an imagecorresponding to each of the divided pupil regions is formed on aphotoelectric conversion surface of the photoelectric conversion unit103 to form an image without a defocus, so that an infinitesimal defectis detected.

As shown in FIG. 14B, photoelectric elements are two-dimensionallyformed in each of the pixel blocks 1031 to 1034. First, pixel blocks ofthe pixel block 1031 will be described. 1031 a to 1031 d denote pixelgroups formed in the pixel block 1031, and cause light from sections W1to W4 at the position of the light spot to be imaged, respectively. 1031a 1 to 1031 aN are pixels belonging to the pixel group 1031 a, and eachpixel outputs a predetermined current when photons are incident. Theoutputs of pixels belonging to the same pixel group are electricallyconnected, and one pixel group outputs a sum of current outputs of thepixels belonging to the pixel group. Similarly, the pixel blocks 1032 to1034 also output a sum of currents corresponding to W-a to W-d. Theoutputs from the respective pixel group, each of which corresponds tothe same section, are electrically connected, and the photoelectricconversion unit 103 outputs an electrical signal corresponding to thenumber of photons detected from a section of each of W1 to W4.

The detection system in FIGS. 13A and 13B are arranged such that along-axis direction of an image of the light spot 20 in thephotoelectric conversion unit 103 coincides with the direction S2′. Asshown in FIG. 8, when S1 and S2 are defined, a vector of the light spotin a length direction is shown represented by (Formula 1).S1=[1,0,0]′  (Formula 1)

Next, when an angle of an optical axis passing through a center of theobjective lens 1021 relative to a vertical direction Z of the sample Wis defined as θ and an angle of the optical axis relative to S2 isdefined as ϕ, a vector representing the optical axis is represented by(Formula 2) (see FIG. 15).D=[sin θ cos ϕ,sin θ sin ϕ,cos θ]′  (Formula 2)

When the light spot 20 is captured from the objective lens 1021, thesame component as the optical axis in S1 is lost. Accordingly, thevector is represented by (Formula 3).S1′=(S1−(S1′·D)D)/∥S1−(S1′·D)D∥  (Formula 3)

A two-dimensional plane excluding the optical axis of the objective lens1021 is divided into two vectors: one having a Z-direction component andthe other one having no Z-direction component (which is shown in(Formula 4) and (Formula 5)).TM=[−cos θ cos ϕ,−cos θ sin ϕ,sin θ]′  (Formula 4)TE=[−sin θ sin ϕ,sin θ cos ϕ,0]′  (Formula 5)

At this time, S2′ in FIGS. 13A and 13B are set in a direction obtainedby being rotated from a vector having no Z-direction componentrepresented by (Formula 5) by an angle represented by (Formula 6).ξ=atan 2(S1′·TM,S1′·TE)  (Formula 6)

S1″ is set so as to be orthogonal to S2′. In this way, the lens array1028 and the photoelectric conversion unit 103 are arranged. A length ofa visual field detected here is defined as L, and a difference Adbetween optical distance of the center of the visual field and the edgeof the visual field is represented by (Formula 7) below.Δd=L/2 sin θ cos ϕ  (Formula 7)

Here, when the numerical aperture of the objective lens 1021 is definedas NA and NA is divided by M via the lens array 1028, a depth of a focusDOF of an image of each lens array is represented as follows.

$\begin{matrix}{{D{OF}} = \frac{\lambda}{2\left( {N{A/M}} \right)^{2}}} & \left( {{Formula}\mspace{14mu} 8} \right)\end{matrix}$

At this time, the interval that can be resolved in the direction S2 isrepresented by the following (Formula 9) based on the size of Airy disk.

$\begin{matrix}{{\Delta\; x_{s\; 2}} = \frac{{0.6}1M\lambda}{{{NA}\left( {1 - \left( {\sin\;\theta\;\cos\;\phi} \right)^{2}} \right)}^{0.5}}} & \left( {{Formula}\mspace{14mu} 9} \right)\end{matrix}$

When M is increased, the resolution represented by (Formula 9) isdeteriorated, and thus the detection sensitivity of a defect decreases.However, when the depth of the focus represented by (Formula 8) isinsufficient for the difference of optical distance in (Formula 7), theresolution at the edge of the visual field is deteriorated due toinsufficient depth of the focus, and thus the detection sensitivity ofthe defect decreases. Therefore, M is typically set to satisfy thefollowing condition of (Formula 10).

$\begin{matrix}{M \approx {{NA}/\left( \frac{\sin\;\theta\;\cos\;\phi\;\lambda}{L} \right)^{0.5}}} & \left( {{Formula}\mspace{14mu} 10} \right)\end{matrix}$

Next, an internal circuit of the photoelectric conversion unit 103 willbe described with reference to FIG. 16. The photoelectric conversionunit 103 that performs output corresponding to the four sections W1 toW4 is described in FIGS. 14A and 14B, but an example in which the foursections are increased to eight sections will be described withreference to FIG. 16.

Eight pixel groups are formed in each of the pixel blocks 1031 to 1034.For example, pixels 1031 a to 1031 h are formed in the pixel block 1031,and groups of the pixel blocks 1032 to 1034 are similarly formed. 1031 a5 is a fifth pixel of 1031 a, and an avalanche photodiode operating inGeiger mode is connected to a signal line 1035-1 a via a quenchingresistor 1031 a 5 q.

Similarly, all the pixels belonging to the pixel group 1031 a areconnected to 1035-1 a, and a current flows through 1035-1 a when photonsare incident on the pixels. 1035-2 a is a signal line to which pixels ofa pixel group 1032 a are connected. In this way, all the pixel groupsare provided with signal lines to which pixels belonging to the pixelgroup are electrically connected. In order to detect scattered lightfrom the same position in the sample W by 1031 a to 1034 a respectively,signal lines of 1031 a to 1034 a are connected to 1035-a via 1036-1 a to1036-4 a, respectively. This signal is connected by a pad 1036-a, and istransmitted to the signal processing unit 105. Similarly, the pixelsbelonging to 1031 b to 1034 b are connected to the signal line 1035-b.The signals are connected by a pad 1036-b, and are transmitted to thesignal processing unit 105.

Here, an equivalent circuit of that of FIG. 16 is shown in FIG. 17.

As shown in FIG. 17, the N pixels belonging to the pixel group 1031 a inthe pixel block 1031, i.e., 1031 a 1 to 1031 aN denote an avalanchephotodiode and a quenching resistor connected thereto. The reversevoltage VR is applied to all the avalanche photodiodes formed in thephotoelectric conversion unit 103 such that all the avalanchephotodiodes operate in Geiger mode. When photons are incident, a currentflows through the avalanche photodiode. However, a reverse bias voltageis lowered due to quenching resistors as a pair, and is electricallydisconnected again. In this way, a constant current flows for everyincidence of photons.

Similarly, N pixels belonging to the pixel group 1034 a in the pixelblock 1034, i.e., 1034 a 1 to 1034 aN also denote an avalanchephotodiode in Geiger mode and a quenching resistor coupled theretosimilarly. All the pixels belonging to the pixel groups 1031 a and 1034a correspond to the reflection or scattered light from the region W-a inthe sample W. All the signals are electrically coupled, and areconnected to a current-voltage conversion unit 103 a. Thecurrent-voltage conversion unit 103 a outputs a signal 500-a convertedinto a voltage.

Similarly, the pixels belonging to the pixel group 1031 b of the pixelblock 1031, i.e., 1031 b 1 to 1031 bN, and the pixels 1034 b 1 to 1034bN belonging to the pixel group 1034 b of the pixel block 1034correspond to light from a surface of a sample W-b, and all the outputsare electrically coupled so as to be connected to a current-voltageconversion unit 103 b. The current-voltage conversion unit 103 b outputsa voltage signal 500-b. In this way, signals corresponding to all theregions obtained by dividing the light spot 20 are output.

FIG. 18 shows a data processing unit 105 when the light spot 20 isdivided into W-a to W-h. 105-lf denotes a block that processes signals500 a-lf to 500 h-lf obtained by photoelectric conversion of lightdetected by a low-angle front detection unit 102-lf. 105-hb denotes ablock that processes signals 500 a-hb to 500 h-hb obtained byphotoelectric conversion of light detected by a high-angle backdetection unit 102-hb. Similarly, a block that processes the outputsignal is provided corresponding to each signal output by eachphotoelectric conversion unit.

1051 a to 1051 h denote a high-frequency pass filter. The outputs of thehigh-frequency pass filters 1051 a to 1051 h are accumulated in a signalsynthesis unit 1053 for a plurality of rotations of the rotation stage,and an array stream signal 1055-1 f is output, which is obtained byadding and synthesizing signals acquired at the same position on thesample W.

1052 a to 1052 h denote a low-frequency pass filter. Similar to 1053, asignal synthesis unit 1054 outputs an array stream signal 1056-lfobtained by adding and synthesizing signals acquired at the sameposition. 105-hb also performs operation similar to that of 105-lf andoutputs an array stream signal 1055-hb synthesized from the outputs ofthe high-frequency pass filters 1051 a to 1051 h and an array streamsignal 1056-hb synthesized from the outputs of the low-frequency passfilters.

A defect detection unit 1057 performs threshold processing afterlinearly adding a signal obtained by linearly adding a signal that isfiltered by a high-frequency pass filter to a signal output by aplurality of photoelectric conversion units. A low-frequency signalintegration unit 1058 integrates signals filtered by the low-frequencypass filters. An output of the low-frequency signal integration unit1058 is input to the defect detection unit 1057 and used for determiningthe threshold value. Typically, the noise is estimated to increase inproportion to square root of the output of the low-frequency signalintegration unit 1058.

Therefore, a threshold value in proportion to the square root of thesignal of the low-frequency signal integration unit 1058 is given afterthe array stream signal of the defect detection unit 1057 is associatedwith the array stream signal of the low-frequency signal integrationunit 1058, so as to extract the signal of the defect detection unit 1057exceeding the threshold value as a defect. The signal of the defectdetected by the defect detection unit 1057 is output to the control unit53 together with signal intensity of the defect and detectioncoordinates on the sample W. The signal intensity detected by thelow-frequency signal integration unit 1058 is also transmitted to thecontrol unit 53 as roughness information of the surface of the sample,and is output to the display unit 54 or the like to a user who operatesthe apparatus.

Second Embodiment

Next, a defect inspection apparatus according to the second embodimentwill be described. A configuration of the defect inspection apparatusaccording to the second embodiment is almost the same as that of thefirst embodiment shown in FIG. 1, and descriptions thereof will beomitted.

The detection unit 102 in the second embodiment will be described withreference to FIGS. 19A and 19B. Unlike the first embodiment, the spot 20is imaged on the photoelectric conversion unit 103 by using the lensarray 1028 and a cylindrical lens array 1029 in a direction orthogonalto the lens array 1028. The cylindrical lens array 1029 separates andforms an image on the photoelectric conversion unit 103 in a directionS1″. Therefore, pixel blocks are two-dimensionally arranged in thephotoelectric conversion unit 103. Eight pixel blocks of 1031-L to1034-L and 1031-R to 1034-R are formed. A signal integration circuit105-pre integrates the photoelectrically converted electrical signalsoutput from the photoelectric conversion unit 103, and transmits theintegrated signals to the signal processing unit 105. Specificprocessing of the signal integration circuit 105-pre will be describedbelow.

FIG. 20 shows a detailed pattern of the photoelectric conversion unit103 in the second embodiment. The eight pixel blocks 1031-L to 1034-Land 1031-R to 1034-R are divided into four pixel block groups. That is,“1031-L, 1032-L”, “1033-L, 1034-L”, “1031-R, 1032-R”, and “1033-R,1034-R”. The pixel blocks belonging to the same pixel block group areelectrically connected between pixel groups corresponding to each other,and pixel blocks are not connected between different pixel block groups.

In the second embodiment, the light spot 20 is divided into eightregions W-a to W-h, and the number of pixel block groups is four, sothat a total of 32 outputs are obtained. That is, the pixel block group“1031-L, 1032-L” outputs currents corresponding to photons detected at500 a-1 to 500 h-1 by electrically connecting outputs of the pixelgroups forming images of the same divided region of the light spot 20.Similarly, “1033-L, 1034-L” outputs currents corresponding to photonsdetected at 500 a-2 to 500 h-2. “1031-R, 1032-R” outputs currentscorresponding to photons detected at 500 a-3 to 500 h-3. “1033-R,1034-R” outputs currents corresponding to photons detected at 500 a-4 to500 h-4.

FIG. 21 is an equivalent circuit of a left half of the sensor describedin FIG. 20, that is, 1031-L to 1034-L. Each of the 103L1 a 1 to 103L1 aNcorresponds to a pixel belonging to a pixel group a, which detectsphotons from the region W-a, in 1031-L, and is configured with anavalanche photodiode and a quenching resistor electrically connectedthereto. 103L1 a 1 to 103L1 aN are connected to a current-voltageconverter 103A1 and output the number of photons, which are convertedinto a voltage, to 500 a-1.

Similarly, 103L1 b 1 to 103L1 bN are a set of avalanche photodiodes andquenching resistors corresponding to the pixels belonging to a pixelgroup b, which detects photons from the region W-b, in 1031-L. 103L1 b 1to 103L1 bN are connected to a current-voltage converter 103B1 andoutput the number of photons, which are converted into a voltage, to 500b-1.

A variable offset voltage regulator 103E1 is connected to thecurrent-voltage converters 103A1 and 103B1. As a result, a reversevoltage applied to 103L1 a 1 to 103L1 a 1N and 103L1 b 1 to 103L1 bN isa difference between VR and an offset voltage applied by 103E1. Sincethe quantity of currents output from the avalanche photodiode in Geigermode corresponds to the reverse voltage applied to the avalanchephotodiode, the voltage of 103E1 is adjusted to control the gain of 500a-1 or 500 a-2 relative to the number of detected photons.

Similarly, each of 103L4 a 1 to 103L4 aN corresponds to a pixelbelonging to a pixel group a, which detects photons from the region W-a,in 1034-L, and is configured with an avalanche photodiode and aquenching resistor electrically connected thereto. 103L4 a 1 to 103L4 aNare connected to a current-voltage converter 103A2 and output the numberof photons, which are converted into a voltage, to 500 a-2.

Similarly, 103L4 b 1 to 103L4 bN are a set of avalanche photodiodes andquenching resistors corresponding to the pixels belonging to the pixelgroup b, which detects photons from the region W-b, in 1034-L. 103L4 b 1to 103L4 bN are connected to a current-voltage converter 103B2 andoutput the number of photons, which are converted into a voltage, to 500b-2. A variable offset voltage regulator 103E2 is connected to thecurrent regulators 103A2 and 103B2, and controls the gain of the voltageoutput by 500 b-2.

As described above, the gain of the voltages output from the pixel blockgroups is individually adjusted. Each pixel block group corresponds to aregion of a pupil of the objective lens 1021 in FIG. 19B. The scatteringdistribution of defects to be inspected and a position of scatteredlight due to roughness of the surface of the sample in a far field areknown. Typically, the scattered light due to surface of the sampleroughness is strongly backscattered, when the defect is a particulatedefect on an upper surface of the sample, the distribution is isotropicdistribution in a low-angle direction, and the sample is mirror-polishedsilicon before a semiconductor pattern is formed. Now, the specificscattered light intensity of the target defect in the far field is setto s (θ, φ), and the roughness scattering from the sample is set to n(θ, φ). When a region of the far field corresponding to a specific pixelblock group i is set to Ω(i), the number of scattered photons detectedby the pixel block group is represented by the following (Formula 11)and (Formula 12).

$\begin{matrix}{{S(i)} = {\sum\limits_{{({\theta,\phi})} \in {\Omega{(i)}}}{s\left( {\theta,\phi} \right)}}} & \left( {{Formula}\mspace{14mu} 11} \right) \\{{N(i)} = {\sum\limits_{{({\theta,\phi})} \in {\Omega{(i)}}}{n\left( {\theta,\phi} \right)}}} & \left( {{Formula}\mspace{14mu} 12} \right)\end{matrix}$

The gain to be applied to the pixel block group is typically shown asthe following (Formula 13).gain(i)∝S(i)/(N(i)+EN(i)²)  (Formula 13)

Here, N(i) represented by (Formula 12) is a roughness noise from thesurface of the sample, whereas EN(i) represented by (Formula 13) is anon-optical noise, typically an electrical noise. 103E1, 103E2 areadjusted to control the gain to be a gain represented by (Formula 13).

FIG. 22 shows integration in the signal integration circuit 105-pre. 500a-1 to 500 a-4 denote outputs corresponding to W-a, which are outputsfrom individual pixel block groups. These outputs are added by an adder105 p-a 0, and 500-a is output. Similarly, 500-b 1 to 500-bN are outputscorresponding to W-b and are added by 105 p-b 0 to output 500-b. 500-h 1to 500-hN correspond to W-h, and are added by 105 p-h 0 to output 500-h.

FIG. 23 shows an embodiment different from that of FIG. 20. FIG. 20shows one chip. However, FIG. 23 shows two chips 103L and 103R, and biasvoltages Vr1, Vr2 are applied to the chips, respectively. The pixelblocks 1031L to 1034L formed in the chip 103L are connected to the pixelblocks 1031R to 1034R formed in the chip 103R, respectively. As aresult, 500 a-3 to 500 h-3 and 500 a-4 to 500 h-4 required in theembodiment of FIG. 20 are unnecessary.

FIG. 24 is an equivalent circuit of the pattern of FIG. 23. 103L1 adenotes a pixel group of a pixel block 103L1 formed in the chip 103L,which corresponds to W-a. 103L1 b denotes a pixel group of the samepixel block, which corresponds to W-b. 103L4 b denotes a pixel group ofthe pixel block 103L4 formed in the chip 103L, which corresponds to W-b.An inverse voltage VR1 is applied to these avalanche photodiodes formedin the chip 103L.

103R1 a denotes a pixel group of the pixel block 103R1 formed in thechip of 103R, which corresponds to W-a. 103R1 b denotes a pixel group ofthe same pixel block, which corresponds to W-b. 103R4 b denotes a pixelgroup of the pixel block 103R4 formed in the chip 103R, whichcorresponds to W-b. An inverse voltage VR2 is applied to these avalanchephotodiodes formed in the chip 103R. An output of 103L1 a iselectrically connected to an output of 103R1 a, and the sum of currentsflowing here is input to the current-voltage converter 103A1. Althoughnot shown, currents, which are output by a pixel group 103L2 a,corresponding to W-a, of the same pixel block group as 103L1, and apixel group 103R2 a, corresponding to W-a, of the same pixel block groupas 103R1, are also input to 103A1 and are converted into a voltage.

Similarly, an output of a pixel group 103L1 b, corresponding to W-b, ofthe pixel block 103L1 of the chip 103L is connected to an output of apixel group 103R1 b, corresponding to W-b, of the pixel block 103R1 ofthe chip 103R, and the outputs are input to 103B1.

Although not shown, currents, which are output by a pixel group 103L2 a,corresponding to W-a, of the same pixel block group as 103R1, and apixel group 103R2 a, corresponding to W-a, of the same pixel block groupas 103R1, are also input to 103A1 and are converted into a voltage.

An output of 103L4 b is electrically connected to an output of 103R4 b,and the outputs are connected to a current-voltage converter 103B2.Although not shown, similarly, 103L3 b is also connected to 103R3 b, andall of the currents in these pixel groups are converted into a voltageby 103B2. 103A1 and 103B1 are connected to the variable offset voltageregulator 103E1. 103E1 is connected to all the current-voltageconverters connected to the pixel groups belonging to the pixel blocks103L1, 103L2, 103R1, and 103R2.

Similarly, all the current-voltage converters connected to the pixelgroups belonging to 103L3, 103L4, 103R3, 103R4 are connected. When avoltage of 103E1 is defined as V1 and a voltage of 103E2 is defined asV2, a voltage of Vr1-V1 is applied to 103L1 and 103L2, a voltage ofVr1-V2 is applied to 103L3 and 103L4, a voltage of Vr2-V1 is applied to103R1 and 103R2, and a voltage of Vr2-V2 is applied to 103R3 and 103R4.Therefore, Vr1, Vr2, V1, and V2 can be combined to apply any voltage toeach image block group.

In the second embodiment, the gain of each pixel block group iscontrolled by the reverse voltages Vr1 and Vr2 applied to the avalanchephotodiode and the offset voltages V1 and V2 of the current-voltageconverter, so as to control the gain. However, the method ofimplementation is not limited to this example. For example, as anotherimplementation method, an analog multiplier for gain control may beprovided for an output of each pixel block group. Alternatively, it isalso possible to apply a commonly known method in which digital input isperformed by an AD converter without gain control, and gain control isperformed by using a digital multiplier after digitization.

Third Embodiment

Next, a defect inspection apparatus according to the third embodimentwill be described. Since a configuration of the defect inspectionapparatus according to the third embodiment is almost the same as theconfiguration of the first embodiment shown in FIG. 1, descriptionsthereof are omitted.

The detection unit 102 in the third embodiment will be described withreference to FIGS. 25A to 25C. A detection unit shown in FIG. 25A has astructure similar to that of the detection unit shown in FIG. 19B.However, the polarization control method of the polarization controlfilter 1022 and the diffuser 1027 are removed, and two lenses 1029, twolenses 1028, and two photoelectric conversion units 103 are provided ona downstream side of the polarization beam splitter 1026.

When the numerical aperture of the objective lens 1021 is increased toefficiently detect scattering from a miniaturized defect by an elementthat changes a state of incident polarization, the polarizationdirection in the far field to which the objective lens 1021 correspondschanges greatly within the aperture. In order to cope with this, thepolarization control filter 1022 is configured with two wave plates: asegmented wave plate 1022-1 (see FIG. 25B) and a half-wave plate 1022-2(see FIG. 25C). The segmented wave plate 1022-1 applies a 180° phasedifference to two orthogonal polarization components using abirefringent material, similar to the half-wave plate. A direction of afast axis is set for each region as indicated in 1022-1 so as tomaximize sensitivity of the assumed defect.

Since the photoelectric conversion units 103-1 and 103-2 are separatelydivided into four pixel block groups, distribution of the fast axischanges discontinuously in correspondence with a boundary of the pixelblock groups typically. The segmented wave plate 1022-1 is generallymanufactured by determining the distribution of the fast axis based on asample to be inspected frequently and a defect type. However, in actualinspection, a composition of the surface of the sample or the defect isdifferent from the assumption. In general, in the case of polarizationcontrol using a half-wave plate, the direction of the fast axis can berotated by a drive mechanism such as a motor to control the polarizationdirection, so that the sensitivity is optimized for an actual inspectiontarget. However, when 1022-1 is rotated, a position of the boundary ofthe pixel block groups deviates from the actual position, which makes itdifficult to optimize.

Therefore, the half-wave plate 1022-2 is provided together with thesegmented wave plate 1022-1. The half-wave plate is provided with arotation drive mechanism for fine adjustment. 1022-1 and the half-waveplate 1022-2 may also be removed from the optical path. The lenses1029-1 and 1029-2 have the same function as the lens array 1029 of FIGS.19A and 19B. The cylindrical lens arrays 1028-1 and 1028-2 also have thesame function as the lens array 1028 shown in FIGS. 19A and 19B. Thephotoelectric conversion units 103-1 and 103-2 also have the samefunction as the photoelectric conversion unit 103 in FIGS. 19A and 19B.The photoelectric conversion unit 103-2 can detect light absorbed by thediffuser 1027 of FIGS. 19A and 19B, and sensitivity of the defect thathave not been focused mainly by the segmented wave plate 1022-1 and thehalf-wave plate 1022-2 may be improved.

Fourth Embodiment

Next, a defect inspection apparatus according to the fourth embodimentwill be described.

Since a basic configuration according to the fourth embodiment is almostthe same as that of the defect inspection apparatus of the firstembodiment shown in FIG. 1, the detailed descriptions thereof areomitted. However, the stage 104 is movable in two directions of XY. Inthe first to third embodiments, scanning is performed while the sample Wis rotated in the θ direction by the stage 104. However, in the fourthembodiment, inspection is performed by scanning the sample W in the Xdirection as shown in FIG. 26.

The detection unit 102 in the fourth embodiment will be described withreference to FIG. 27.

In the fourth embodiment, a defect on the sample W on which a pattern isformed is detected. The detection unit 102 has a relatively smallaperture in FIGS. 25A-25C. The detection unit 102 includes a pluralityof detection systems in one apparatus as shown in FIG. 10, but thedetection unit 102 includes one lens whose numerical aperture approaches1 in FIG. 26. The objective lens 1021, the polarization control filters1022-1 and 1022-2, the polarization control filter 1023, the aperture1024, the condenser lens 1025, and the polarization beam splitter 1026have the same functions as those with the same number shown in FIGS.25A-25C.

The polarization beam splitter 1026 splits the optical path based on thepolarization component. 10210-1 to 10210-3 denote a spatial filter whichis typically configured with a plurality of rods that can be moved to adiffracted light position by a motor so as to shield diffracted lightfrom a pattern. 10211 denotes a perforated mirror.

FIG. 28 is a Y-Z plan view of the perforated mirror 10211. The lighthaving passed through the aperture is directed to the spatial filter10210-3, and the other light is directed to the spatial filter 10210-2.1028-1 to 1028-3 denote a cylindrical lens array and are arranged in avicinity of a position where a pupil of the objective lens 1021 isoptically relayed. The lens arrays 1028-1 to 1028-3 image a plurality ofimages of the beam spot 20 on the photoelectric conversion units 103-1to 103-3, respectively.

FIG. 29 shows the lens array 1028-1. The lens arrays 1028-1-α to1028-1-γ image the images of the scattered light of the far field,corresponding to the arrangement, on photoelectric conversion units103-1-α to 103-1-γ respectively, which are a TDI sensor on thephotoelectric conversion unit 103-1 shown in FIG. 30. The TDI sensormoves and accumulates charges in synchronization with scanning for W,and outputs pixels divided in the Y direction. Similarly, thephotoelectric conversion units 103-2 and 103-3 capture images andtransfer the images to the signal processing unit 105 to detect adefect.

Fifth Embodiment

In the fifth embodiment, an imaging unit 102-A2 shown in FIG. 13B isadopted as another configuration of an imaging unit 102-A1 shown in FIG.13A.

In the configuration of the imaging unit 102-A1 shown in FIG. 13A, aplurality of images are formed on the photoelectric conversion unit 103by one lens array 1028. However, in the imaging unit 102-A2 according tothe fifth embodiment shown in FIG. 13B, imaging is performed by usingthree lens arrays 1028 a, 1028 b, and 1028 c and one cylindrical lens1029 a.

First, 1028 a and 1028 b denote lens arrays for magnificationadjustment, and 1028 c denotes a lens array for imaging. 1028 a and 1028b denote a Kepler magnification adjustment mechanism. The Keplermagnification adjustment mechanism is used here, but other adjustmentmechanisms such as a Galileo magnification adjustment mechanism may beused without being limited to this example.

In the configuration of the imaging unit 102-A1 without the lens array1028 a and the lens array 1028 b, a magnification error occurs in eachimage formed by the lens array 1028.

The magnification error will be described with reference to FIGS. 32Aand 32B.

An angle formed between a light beam incident on the objective lens 1021and the optical axis is defined as θ1. An angle formed between thesample W and the optical axis is defined as θ2. Here, it is assumed thatthe light beam incident in θ1 passes through a center of one lens amongthe lenses constituting the lens array 1028 at a position where thepupil of 1021 is relayed. An angle formed between a light ray and thesurface of the sample is represented by θ3, which is represented by thefollowing (Formula 14).sin θ3=(1−((cos θ1−sin θ1)(−sin θ2 cos θ2)^(T))²)^(0.5)  (Formula 14)

Images formed on positions 10421 to 10423 of alight receiving surface103 have a size proportional to sin θ3(i) that is calculated from adirection θ1(i) of a principal light ray incident on a lens i of 1028for forming an image.

Here, FIGS. 33 to 35 show intensity profiles of images of a sphericalbody with a minute size in the sample W. FIGS. 33 to 35 show profiles ofimages formed on 10421, 10422, and 10423, respectively.

10421 a to 10421 c correspond to 1041 a to 1041 c, respectively.Similarly, 10422 a to 10422 c, and 10423 a to 10423 c are intensityprofiles of images corresponding to 1041 a to 1041 c.

The intensity profiles shown in FIGS. 33 to 35 are formed by differentlenses constituting the lens array 1028. Therefore, θ1 (i) is different,so that sin θ3(i), which is a value proportional to the magnification,changes. When the numerical aperture of 102 increases, a change of θ1becomes larger in the same lens. Accordingly, the change inmagnification increases.

The thus-formed image is formed on the photoelectric conversion unit 103shown in FIG. 16. For example, when pixels are connected to a signalline 1035-a, resolution of the image decreases when a pitch of thepixels formed in the pixel blocks 1031 to 1034 is constant. Therefore,pitches of pixels of the pixel blocks 1031 to 1034 are set in proportionto magnification corresponding to each pixel block. This can be realizedby setting a pitch proportional to sin θ3(i) calculated by (Formula 14).

Sixth Embodiment

The fifth embodiment describes a method of preventing a decrease inresolution of an image due to a variation in magnification by adjustinga pitch of pixels constituting a pixel block corresponding tomagnification of an image formed by a lens constituting the lens array1028. However, when the pitch of pixels is changed, electrical capacityof the pixel changes, and frequency response output from the pixelchanges for each signal line. Accordingly, a high-frequency component ofa signal pulse tends to be lost over time.

Therefore, in the sixth embodiment shown in FIGS. 36A-36C, themagnification is corrected by a Kepler magnification adjustmentmechanism. As shown in FIG. 36A, the lens array 1028 a is configuredwith cylindrical lenses 1028 a 1 to 1028 aN. Similarly, the lens array1028 b is configured with cylindrical lenses 1028 b 1 to 1028 bN. Whenfocal lengths of cylindrical lenses of 1028 a 1 to 1028 aN are set asfa(1) to fa(N) and focal lengths of cylindrical lenses of 1028 b 1 to1028 bN are set as fb(1) to fb(N), a focal length is set under thefollowing conditions.∀i,fa(i)+fb(i)=C1  (Formula 15)∀i,fa(i)sin θ3(i)/fb(i)=C2  (Formula 16)∀i,fb(i)<fa(i)  (Formula 17)

Here, C1 and C2 denote constants and design parameters. (Formula 15) isa necessary condition for all of the lenses constituting 1028 a and 1028b to satisfy the conditions of the Kepler magnification adjustment.

(Formula 16) is a condition for correcting magnification that variesdepending on an incidence direction toward a pupil and for makingmagnification of formed images same. (Formula 17) is a condition forpreventing light beam from being larger than an aperture diameter of alens in the lens array 1028 b, and for preventing occurrence of adecrease in transmittance.

After the magnification is adjusted in this manner, intensity profilesof images of 1041 a to 1041 c imaged at 10424 are denoted by 10424 a to10424 c (see FIG. 36B). In addition, similar profiles at 10425 aredenoted by 10426 a to 10426 c (see FIG. 36C). The profile in 10424becomes thick since the magnification is increased. However, distancebetween peaks matches the image formed by any lens.

Accordingly, a pitch of patterns in the photoelectric conversion unit,for example, a pixel pitch formed in pixel blocks denoted by 1031 to1034 in FIG. 16 may be in a constant state. 1028 c denotes an imaginglens, and focal lengths of the cylindrical lenses constituting theimaging lens 1028 c are all the same.

A cylindrical lens 1029 a is in a direction orthogonal to imagingdirections of the cylindrical lenses 1028 a to 1028 c. The arrangementof the cylindrical lens 1029 a will be described below in a seventhembodiment having the same structure.

Seventh Embodiment

FIGS. 37 and 38 show arrangement of an optical system, which is anotherembodiment of the detection unit 102B in FIGS. 19A and 19B, fromdifferent viewpoints.

In the configuration of the detection unit 102B in FIGS. 19A and 19B,1029 denotes a cylindrical lens array, and is arranged at a positionwhere the pupil of 1021 is relayed. However, since the cylindrical lensarray 1028 is required to be arranged at the pupil, arrangement ofoptical components interferes. Accordingly, any of the lenses isrequired to be displaced from the pupil.

In the seventh embodiment, 1029 a is used instead of 1029 to controllight in a direction S1″. 1029 is arranged at a pupil, and imaging isperformed by each of two cylindrical lenses constituting 1029. In theseventh embodiment, when an image of light distribution in the directionS1″, the light is not separated by lens arrays, and instead it ispossible to form an image divided by a pupil equal to 1029. In adirection S2′, similar to the sixth embodiment, light in a pupil isseparated and forms an image by the lens arrays 1028 a, 1028 b, and 1028c arranged at positions where the pupil is relayed.

Eighth Embodiment

Another configuration of the detection unit 102 c of FIG. 25A is shownin FIG. 39.

1028-1 a to 1028-1 c and 1028-2 a to 1028-2 c have the sameconfiguration and function as 1028 a to 1028 c in the sixth embodiment.1029-1 a and 1029-2 a have the same configuration and function as 1029 ain the seventh embodiment.

According to the configuration of the eighth embodiment, it is possibleto prevent variation in magnification generated by the direction of thelight beam incident on the objective lens 1021 in the configuration ofFIGS. 25A-25C. In addition, interference of the optical component at apupil position can also be prevented.

According to the above embodiments, the optical path is divided by anoptical dividing unit arranged at a pupil position of a condensing unitor at or in a vicinity of a position where the pupil is relayed.Accordingly, an image having a numerical aperture that is relativelysmall relative to the numerical aperture of the first-stage condensingunit may be formed on the photoelectric conversion unit. As a result,the depth of the focus is increased, and thus imaging detection from adirection that is not orthogonal to the longitudinal direction of theillumination may be performed. That is, an imaging detection system canbe arranged without being restricted by an azimuth angle, and images ofthe entire light scattered from an infinitesimal defect that exists onthe surface of the sample can be substantially captured. In this way,the defect that exists on the surface of the sample can be detected withhigh accuracy by a defect inspection apparatus.

REFERENCE SIGNS LIST

-   2 light source-   5 beam expander-   6 polarization control unit-   7 illumination intensity distribution control unit-   24 illumination intensity distribution monitor-   53 control unit-   54 display unit-   55 input unit-   101 illumination unit-   102 detection unit-   103 photoelectric conversion unit-   104 stage unit-   105 signal processing unit-   1021 objective lens-   1022 polarization control filter-   1023 polarization control filter-   1024 aperture-   1025 condenser lens-   1026 polarization beam splitter-   1027 diffuser-   1028 lens array

The invention claimed is:
 1. A defect inspection apparatus comprising:an illumination unit configured to illuminate an inspection objectregion of a sample with light emitted from a light source; a detectionunit configured to detect scattered light in a plurality of directions,which is generated from the inspection object region; a photoelectricconversion unit configured to convert the scattered light detected bythe detection unit into an electrical signal; a signal processing unitconfigured to process the electrical signal converted by thephotoelectric conversion unit to detect a defect in the sample, whereinthe detection unit includes an imaging unit configured to divide anaperture and form a plurality of images on the photoelectric conversionunit, an objective lens configured to converge the scattered lightgenerated from the inspection object region; an imaging lens configuredto form an image of the light converged by the objective lens at apredetermined position; a condenser lens configured to converge theimage formed by the imaging lens; a lens array including a plurality ofarrays and configured to divide an image converged by the condenser lensby the plurality of arrays to form the plurality of images on thephotoelectric conversion unit; and, the signal processing unit isconfigured to synthesize electrical signals corresponding to theplurality of formed images to detect a defect in the sample.
 2. Thedefect inspection apparatus according to claim 1, wherein the detectionunit further includes: an aperture that is arranged at the predeterminedposition and shields a region, where photoelectric conversion is notperformed by the photoelectric conversion unit, in the image formed bythe imaging lens.
 3. The defect inspection apparatus according to claim1, wherein the photoelectric conversion unit includes a plurality ofpixel blocks corresponding to the plurality of arrays of the lens array,and the imaging unit forms the plurality of images on the plurality ofpixel blocks of the photoelectric conversion unit respectively.
 4. Thedefect inspection apparatus according to claim 1, wherein the inspectionobject region is divided into a plurality of inspection regions, thepixel block is configured with a plurality of pixel groups respectivelycorresponding to the plurality of inspection regions obtained bydividing the inspection object region, each of the pixel groups includesa plurality of pixels arranged in a line shape, and the photoelectricconversion unit electrically connects the plurality of pixels andsynthesizes photoelectric conversion signals output by the plurality ofpixels to output the electrical signals.
 5. The defect inspectionapparatus according to claim 1, wherein the lens array is arranged at aposition where a pupil of the objective lens is relayed, and theplurality of arrays divide the pupil of the objective lens and forms theimage on the photoelectric conversion unit for each of the pupil regionsobtained by dividing the pupil.
 6. The defect inspection apparatusaccording to claim 1, wherein the lens array is arranged at a pupilposition of the condenser lens.
 7. The defect inspection apparatusaccording to claim 1, wherein the lens array is arranged at a rear focalposition of the condenser lens.
 8. The defect inspection apparatusaccording to claim 4, further comprising: a gain control unit configuredto determine output intensity of the electrical signal corresponding toa quantity of light input to the pixels for each pixel group of thepixel block in the photoelectric conversion unit.
 9. The defectinspection apparatus according to claim 8, wherein the photoelectricconversion unit is configured with an avalanche photodiode formed foreach of the pixels, and the gain control unit controls an inversevoltage to be applied to the avalanche photodiode.
 10. A defectinspection method comprising: an illumination step of illuminating aninspection object region of a sample with light emitted from a lightsource; a light detection step of detecting scattered light in aplurality of directions, which is generated from the inspection objectregion; a photoelectric conversion step of converting the detectedscattered light by a photoelectric conversion unit into an electricalsignal; and a defect detection step of processing the convertedelectrical signal to detect a defect of the sample, wherein an apertureof an imaging unit is divided to form a plurality of images on thephotoelectric conversion unit in the light detection step, electricalsignals corresponding to the plurality of formed images are synthesizedto detect a defect of the sample in the defect detection step, aplurality of pixel blocks are formed in the photoelectric conversionunit, the plurality of images are formed on the plurality of pixelblocks of the photoelectric conversion unit respectively, wherein theinspection object region is divided into a plurality of inspectionregions, the pixel block is configured with a plurality of pixel groupsrespectively corresponding to the plurality of inspection regionsobtained by dividing the inspection object region, the pixel group isconfigured with a plurality of pixels arranged in a line shape, and thephotoelectric conversion unit electrically connects the plurality ofpixels, and synthesizes photoelectric conversion signals output by theplurality of pixels to output the electrical signals.
 11. The defectinspection method according to claim 10, further comprising: a step ofdetermining output intensity of the electrical signals eachcorresponding to a quantity of light input to the pixel for each pixelgroup of the pixel block of the photoelectric conversion unit.
 12. Thedefect inspection method according to claim 11, wherein thephotoelectric conversion unit is configured with an avalanche photodiodeformed for each of the pixels, and the output intensity of theelectrical signal is determined by controlling a reverse voltage to beapplied to the avalanche photodiode.
 13. The defect inspection apparatusaccording to claim 1, wherein the imaging unit forms each of theplurality of images obtained by dividing the aperture at magnificationdetermined for each image on the photoelectric conversion unit.
 14. Thedefect inspection apparatus according to claim 1, wherein in thephotoelectric conversion unit, a pitch of pixels formed in thephotoelectric conversion unit is set according to magnification of animage formed on the photoelectric conversion unit.
 15. The defectinspection apparatus according to claim 1, wherein the imaging unitforms an image of the inspection object region in one direction and animage of a position of a pupil of the objective lens in anotherdirection different from the one direction, at magnification determinedfor each image on the photoelectric conversion unit.
 16. The defectinspection apparatus according to claim 1, wherein the imaging unitforms an image of the inspection object region in one direction and animage of a position of the objective lens where a pupil thereof isrelayed in another direction different from the one direction, atmagnification determined for each image on the photoelectric conversionunit.